1. Field of the Invention
The present invention relates to a method for automatic parallax determination in connection with stereoscopic optical system preferably those having two eyepieces and having at least one movable grating structure in the imaging light path, such as is used in connection with a base range finder, for example, using electrical signals which are derived from differentiable luminous fluxes of such an optical system. The invention further relates to an optical system which is adapted for the application of such a method.
2. Description of the Prior Art
In stereoscopic optical systems, it is generally desirable that the parallax between two partial images be determined automatically. This is particularly so in the case of base range finders, or in connection with the analysis of aerial stereo photographs. Various systems for optical-electrical scanning and for the subsequent use or processing of the resulting electrical signals have already been suggested for these purposes.
Such a prior art system is shown in FIG. 1 of the drawing, where the fundamental wave of the resulting signals is being utilized. Two objective lenses 10 and 11, which define two light channels, project an image of an object (not shown) onto a grating structure 16, via the deflecting mirrors 12, 13, 14 and 15. The grating structure 16 is movable perpendicularly with respect to the optical axes 18 and 19 by means of a drive 17' which is controlled by a generator 17. In each optical axis is arranged a photoelectric receiver 20 or 21, respectively, which produces an electrical signal responsive to the light portions which have passed through the grating structure 16. To each of the two receivers 20 and 21 is connected a phase discriminator or comparator 22 or 23, respectively, which is controlled by means of a reference signal received from the generator 17, and the output of the discriminator 22 of the first light channel is connected to the drive 17' of the grating structure 16, via a control member 24. The exit of the discriminator 23 controls an adjustment mechanism 25, via a control member 26. The mechanism 25 provides mechanical means for pivoting the mirror 15 along the direction of the arrow as indicated.
The operation of the system of FIG. 1 is such that the first light channel determines the position phase differential and, with the aid of the control member 24, shifts the median position of the grating structure 16 until it reaches the point where the output signal of the phase discriminator 22 reaches zero. At this point, the phase discriminator 23 indicates the parallax. The control member 26 and the drive 25 for the mirror 15 serve to adjust the resultant parallax to zero.
One shortcoming of this prior art system is that it requires two feedback loops which are coupled over the grating structure.
In U.S. Pat. No. 3,710,124 is described a method which uses the fundamental wave and the second harmonic of the grating frequency. A shortcoming of the method disclosed in this patent, as can be demonstrated, is that the accuracy of the measurements obtainable is dependent upon the accuracy with which the amplification has been adjusted, and the latter, in turn, is influenced by the amplitudes of the fundamental wave and of the second harmonic.